NATURAL HISTORY

Habitat & vegetation
The Brenton Blue (Figure 8 below) needs a particular habitat for its survival. It lives in a high rainfall area on a south facing dune slope quite close to the sea. The vegetation is a mixture of asteraceous (daisy family) coastal fynbos and coastal thicket. Trees, such as candlewood, on the site provide partial shade that the butterfly seems to prefer for plants on which to lay its eggs.

© D Britton

Figure 8 – O. niobe female

Figure 9 – Mating pair of O. niobe

Life cycle
The adult butterflies hatch out in late October and November, living for only 2-3 weeks. The males establish and patrol territories, seeking and attracting females to mate with (Figure 9 above). The females advertise their presence by emitting pheromones, which attract the males. The fertilised female lays its 0.6mm dia white eggs (Figure 10 below) singly on the underside of the leaves of the food plant on which its larvae (caterpillars) feed, whose scientific name is Indigofera erecta. This is a member of the legume (pea) family, with a small pink flower (see Figure 4). There are two other Indigofera species in the reserve with similar-looking flowers, but this butterfly does not use these species.

© D A Edge

Figure 10 - Ovum (egg) of O. niobe on food plant

Figure 11 - First instar larva of O. niobe

© D A Edge

Figure 12 - Third instar larva of O. niobe

Figure 13 - Woody rootstock and larval feeding marks

The larva hatches out of the egg (Figure 10 above) after about ten days (Figure 11 above) and feeds on the leaflets of the food plant until after its second moult, when it reaches the third instar stage (Figure 12 above). It then crawls down the stem of the plant to the ground and encounters Camponotus baynei ants, which attend the larvae and give it protection from predators. The larvae produce highly palatable and nutritious secretions from honey glands in their skin, on which the ants feed. The ants excavate a hole around the rootstock of the plant (Figure 13 above), and the larva crawls down onto the rootstock on which it starts feeding. The larvae have a final development stage (the fourth instar - see Figure 14 below) during which they grow to 15-20mm in length before pupating (forming a chrysalis or pupa) in the hole alongside the rootstock.

The host ants, C. baynei, nest in dead wood lying on the ground (see Figure 15 below). The ants that tend the larvae are foraging ants that return to the nest to share the nutritious exudations of the O. niobe larvae with their own young.

From the eggs laid in October and November, adults hatch out in the following January/ February. Sometimes there is a small third brood in April if weather conditions are favourable.

Figure 14 - Fourth instar larva of O. niobe

Figure 15 - Nest of Camponotus baynei ants in dead wood, showing worker ants and grubs